Headlamps, and in particular, projector-type headlamps have been provided for vehicle illumination applications, and their structure is well known in the art. A conventional vehicle headlamp includes a light source and optical components, such as lenses and reflectors to collect and shape light emitted by the light source and to project the resulting beam pattern forward of the vehicle.
It is preferred that a single headlamp system be capable of projecting more than one beam pattern. For example, a headlamp system may project a low beam pattern and a high beam pattern. Such a bifunctional system is conventionally provided by utilizing multiple-filament light sources: one filament for the low beam function, and another for the high beam function. Other conventional bi-functional projector systems utilize a single shutter or light shield to selectively block a portion of the light from a single-filament light source to provide a low beam pattern. To provide a high beam pattern, the shielded light is added to the beam by retraction of the shield.
One limitation of these types of conventional bi-functional projector systems (using single-shield actuation) is that the systems do not achieve unique low and high beam patterns. In the United States, automotive lighting devices are regulated under Federal Motor Vehicle Safety Standard 108 (“FMVSS108”), which specifies, for example, photometric requirements for dual-filament light sources. In order to qualify under FMVSS108 as a dual-filament light source, the low beam pattern and the high beam pattern must be sufficiently distinct. Because conventional bi-functional projector systems provide beam patterns that lack the optimal low to high beam contrast ratio, such systems do not conform to FMVSS108. This has significantly hindered the implementation of bifunctional projector lamp systems that use sources other than HID (e.g., halogen light sources).
In view of the foregoing, there exists a market need for a compact bi-functional projector style headlamp system using a single-filament light source. The novel projector lamp should provide a high contrast ratio between the low and high beams.